Differences Between ERW Steel Pipe and HFW Steel Pipe
The didderence of ERW, HFW welding processes.
ERW welding process refers the heat generated by the resistance to current flowthat pass through the jointed metals. So a large current is
needed to electrify the whole surface of the steel plate or coil to the length of welding. In the ERW welding process, the electric current that
pass through the entire conductor is at 50/60 Hz.
HFW welding process is not the same case with the high-frequency process, since it is only a section of the steel metals is heated by the
induction of electric coil. High-frequency is generated by either AC or DC current. In these cases, the constant current welding generator and
constant voltage high-frequency welding generator are used.
Constant current welding machine generates power in 100-800 kHz. In the elder processes, the conversion of 60 Hz. AC current to HF was
done by using triode and tank circuits. New welding machine usesmetal oxide silicon, filed-effect transistors, usually associated with parallel
resonant circult. The constant voltage version generators use insulated gate bipolar transistors designed to power about 2000 kW with
frequency rages of 100-600 KHz.
HFW is required in API 5L PSL2 ERW steel pipe
According the API 5L and ISO 3183 specification, for PSL2 pipes in welded process the HFW welding is a mandatory requirements for ERW
steel pipes. As it is an improvement from the inherent problem of hardness, lack of fusion and susceptibility of stress corrosion cracking(SCC)
ERW steel pipe includes HFW steel pipe
ERW is general designation of resistance welded steel pipes. It can be sorted into two types: alternated current welding(AC) and direct current
welding(DC). According to different frequency, AC welding can be divided into low frequency welding intermediate frequency welding, ultra
frequency welding and high frequency welding. The high frequency welding (HFW) is mainly used in ordinary or thin wall steel pipe. It includes
contact welding and induction welding. Directcurrent welding is generally used for small caliber steel tubes in general, HFW is one of ERW production
methods, it adopts the high frequency welding process. So ERW includes HFW steel pipe.
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